Republicans have just one real shot at unseating a Democratic senator this year, and on Tuesday they will find out how realistic their chances are.
Depending on who wins Tuesday's primary, the party will either have to get behind a self-funder who used to be a Democrat, a businessman who wants to go beyond Trump's Muslim ban, a young Air Force Reserve major whose campaign contractor forged signatures to get on the ballot, a former TV analyst who lost a 2010 bid for Congress by double digits, or a county commissioner with an all-volunteer staff who's been backed by Ted Cruz and Sarah Palin.
The choice is overwhelming. A field that began with about a dozen candidates still has five contenders, and without any public polling, there's little consensus over who has the upper hand.
"No candidate is dominating, and really anything is possible," said Steve Gordon, political director for Colorado's junior senator Cory Gardner's 2014 campaign.
Regardless of who emerges as the nominee on Tuesday, the Democratic incumbent, Sen. Michael Bennet, begins as the clear favorite in the general election in a state that has gone blue at the presidential level the last two times.
He's had months to reintroduce himself to voters through a series of positive ad spots. And he's got plenty of money to keep doing that — he ended the pre-primary FEC reporting period with $5.7 million.
The eventual GOP nominee will not only have Bennet's war chest to contend with. He will also have to run on the same ticket as Donald Trump — a daunting task in a state with a growing Hispanic population .
The two candidates whose self-funding could put them the closest to Bennet in terms of resources are Jack Graham, former athletic director of Colorado State University, and businessman Robert Blaha .
The two candidates have kicked significant personal money into their campaigns, allowing them to be on air the most. They likely enjoy the highest name recognition too — and that, Republicans say, could be the determining factor in this race.
Graham spent more than any other candidate during the pre-primary reporting period, followed by Blaha. Graham has loaned his campaign $1.5 million so far , and he ended the pre-primary reporting period with $883,000.
"Many voters tuned in late this campaign and almost deliberately withheld their decision to vote" because of how many little-known candidates made up the field, said former state GOP chairman Dick Wadhams, who is currently Graham's campaign manager.
Wadhams is optimistic that his candidate's air and mail campaign will have won over voters' attention at the last minute.
Graham's ads are low quality and focus mostly on a business message. "I'm not a lawyer, never run for office and don't owe any favors in Washington," Graham says in one ad .
A moderate who supports abortion rights, Graham was a registered Democrat until recently. His campaign has explained that he was a Democrat "by family tradition," and that he had long supported Republican candidates but was too busy to change his registration.
Unlike Graham, Blaha has embraced Trump. He made national news when he said that he'd like to "go beyond just Muslims" when it comes to banning certain people from entering the country.
He shares some of Trump's blunt, provocative tone. One of his first ads refers to "bozos like Michael Bennet" and shows a man getting a rectal exam. And he's pledged not to seek re-election if Congress doesn't reduce illegal immigration by 50 percent.
Blaha has loaned his campaign $1 million. This isn't his first campaign. He lost a 2012 Republican primary to 5th District Rep. Doug Lamborn.
Blaha has vowed not to self-fund this Senate campaign as much as he did in his 2012 race, and he ended the pre-primary period with only $278,000.
Likely close behind Graham and Blaha in name identification is former State Rep. Jon Keyser , a major in the Air Force Reserves.
Keyser has loaned his campaign much less — $150,000 — and ended the pre-primary campaign with just $173,000 in the bank . That's a far cry from the $3 million he said he received in soft money pledges when he attended the Republican Jewish Coalition's Presidential Forum in Washington, D.C., late last year.
Keyser was long touted as the establishment candidate, and his allies talked up his "made-for-TV" qualities. But drawn-out problems with his ballot signatures have blemished that reputation .
Several candidates struggled with ballot signatures. Former Aurora City Councilman Ryan Frazier barely made it on the ballot.
Frazier lost to Democratic Rep. Ed Perlmutter in 2010. As a result of that previous run and his tenure as a local TV political analyst, he may enjoy some additional name recognition.
"He's a longer shot," Gordon said, "but not an impossible one."
Frazier has loaned $148,000 to his campaign, and he spent $228,000 during the pre-primary period. But he doesn't have much left. He ended the pre-primary reporting period with just $20,000.
Only El Paso County Commissioner Darryl Glenn qualified for the ballot by winning the backing of the state GOP convention, a gathering of mostly dedicated conservatives. Senate Conservatives Fund and FreedomWorks have endorsed him, as well as Texas Sen. Ted Cruz. Sarah Palin's PAC cut his campaign a $5,000 check earlier this month.
Glenn ended the pre-primary period with only $50,000. He likes to run a lean campaign — so lean, in fact, that his staff are all volunteers .
Voters in the Centennial State have already started early voting to select their Senate nominee. This marks the only the second statewide primary where all votes will be cast be mail.